Roll-to-roll patterning of Al/Cu/Ag electrodes on flexible poly(ethylene terephthalate) by oil masking: a comparison of thermal evaporation and magnetron sputtering

Abstract

Here we show in-line-patterning of Al (37 nm)/Cu (58 nm)/Ag (55 nm) electrodes on flexible poly(ethylene-terephthalate) at 1–25 m min−1, using a flexography printing apparatus retrofitted to a commercial roll-to-roll vapor deposition system. A Krytox® 1506 lift-off mask was printed for simultaneous evaporation during metal deposition. Heat through Al thermal evaporation facilitated single-step patterning with 99.99% masking efficiency, and 5% area shrinkage compared to the 4 × 6 mm photopolymer stamp. Al with nominal line widths of 28–58 μm (average. 47 μm) was also demonstrated using a commercial nitrile sleeve. Sputtering was trialed using powers 1–2 kW, substrate speeds of 1–25 m min−1, and was unable to achieve mask lift-off, leading to metallic over-coating, removed via secondary isopropanol cleaning. Dynamic deposition rates of thermal evaporation exceeded sputtering (928 vs. 775 nm·m min−1 respectively, with ten inline/confocal sputtering sources theoretically required). Resistivities of Al/Cu/Ag were 7.2 × 10−8/8.2 × 10−7/6.8 × 10−8 Ω·m; 2.6/48.2/4.2× greater than respective bulk values whilst work functions of electrodes varied 4.21/4.93/5.22 eV. Resistivities were critically impaired in proximity/on sputtered Cu/Ag. Electrodes were “printed” without inks/post-deposition heat-treatments, and whilst challenges remain, selective metallization is ready for high-throughput flexible electronics whilst sputtering may be used in a two-step process, requiring additional development for single-step patterning.